It is already known in the art to coat textiles such as woven or knitted fabrics and non-woven bonded webs with solutions of polyurethanes by the direct or the reversal process. The articles obtained are used for the manufacture of outer-wear garments, upholstery goods, luggage, shoe uppers, tents and tarpaulins, blinds and many other products.
In contrast to the two-component polyurethanes, which have been known for some time, the so-called one-component polyurethanes have been more recently introduced into the art. These products are obtained by the reaction of polyhydroxyl compounds, in practice mainly dihydroxy polyesters or dihydroxy polyethers, in combination with glycols, preferably butane diol-(1,4), and aromatic diisocyanates, preferably 4,4'-diphenylmethane diisocyanate as described in German Patent Specification No. 1,106,959 and German Auslegeschrift No. 1,112,291. Solutions of one component polyurethanes have a practically unlimited pot life. Formation of films from these polyurethanes is a purely physical process which, in contrast to the formation of films from two-component polyurethanes, is not accompanied by any chemical cross-linking reaction.
In contrast to chemical cross-linking, physical cross-linking is reversible, which means that one-component polyurethanes are thermoplastically deformable. This inevitably renders textile coats containing one-component polyurethanes to some extent sensitive to deformation by pressure at elevated temperatures. One consequence of this is that, in certain fields of application, for example in the manufacture of shoe uppers, these materials are insufficiently able to withstand ironing because the coating undergoes thermal deformation by pressure even below its melting range and irreversibly penetrates the fabric ("penetration by ironing" of the fabric structure).
An improvement in the resistance to ironing can generally be obtained by elevating the temperature range at which the polyurethane melts. The usual methods employed for elevating the polyurethane melting range are based, for example, on increasing the proportion of hard segments by using a higher molar proportion of chain-lengthening agents, by incorporating short, compact hard segments by using short chain glycols, preferably ethylene glcyol, as chain-lengthening agent, or by incorporating high melting aromatic hard segments, for example by using 1,4-phenylene-bis-(.beta.-hydroxyethyl ether) as chain-lengthening agent. Unfortunately, this known method of elevating the polyurethane melting range invariably reduces the solubility of the polyurethanes in the usual commercial solvent combinations so that the resulting solutions are more or less viscous and in many cases even tend to be pasty and are difficult or even impossible to process in the usual coating installations.
It is known from German Auslegeschrift No. 2,161,340 and German Offenlegungsschrift No. 2,402,799 which corresponds to U.S. Ser. No. 542,734, filed Jan. 20, 1975 to Thoma et al. that the solubility of one-component polyurethanes can be improved by using an equimolar mixture of at least two different glycols instead of a single glycol as chain-lengthening agent. Unfortunately, however, the use of such mixtures of chain-lengthening agents significantly lowers the polyurethane melting range so that the dimensional stability at elevated temperatures and hence the resistance to ironing of the polyurethane coatings are again reduced.